This invention relates to an improved process for hydroconverting carbonaceous materials to lower molecular weight products. More particularly, this invention relates to an improved catalytic process for hydroconverting carbonaceous materials to lower molecular weight, liquid products.
Heretofore, several catalytic processes for hydroconverting carbonaceous materials such as petroleum residuum, coal, lignite, peat and the like to lower molecular weight products have been proposed. In general, the lower molecular weight products may be either gaseous or liquid or a mixture of both. The production of lower molecular weight liquid products is, however, particularly desirable since liquid products are more readily stored and transported and, often, are conveniently used as motor fuels.
Heretofore, a large number of suitable catalysts have been identified as useful in such hydroconversion processes. For example, metal sulfides and oxides and mixtures thereof have been particularly useful as catalysts in such processes. Moreover, a host of catalyst precursors; i.e., compounds that will either decompose or are readily converted to an active sulfide or oxide form, have been identified. Such precursors include metal complexes such as transition metal hydrocarbyl-substituted dithiocarbamates, transition metal naphthenates and phospho-transition metal acids and inorganic compounds such as ammonium salts of transition metals. In general, the precursors used have either been soluble to some extent in the reaction medium itself or in a solvent which is added to the reaction medium. The solvents heretofore employed have been both organic and inorganic.
Heretofore, it has also been proposed to use iodine to enhance the hydroconversion of carbonaceous materials such as coal in thermal operations. In processes of this type, relatively high concentrations of iodine are employed. The enhancement of the hydroconversion is believed to be due to the formation of HI from I.sub.2 in the presence of hydrogen. The HI is then instrumental in the formation of a hydrogen radical (H.) which participates in the hydrogenolysis reaction to break bonds in the carbonaceous material which normally cannot be broken thermally to form a lighter (lower molecular weight) product.
Notwithstanding that a large number of suitable catalysts for the hydroconversion of carbonaceous materials have been identified and, notwithstanding that the yield of liquid product has been relatively high, when compared to liquid yields in thermal operations, with the better of these catalysts particularly catalysts comprising molybdenum, the yield of naphtha boiling range material which may be used directly or upgraded and then used as motor gasoline has been low. As a result, it has, heretofore, been necessary to further process the higher boiling liquid products such as middle distillate and vacuum gas oil to further increase the yield of gasoline range boiling liquid products. This additional treatment, however, further complicates the hydroconversion process, significantly increases the molecular hydrogen required to effect the conversion and significantly increases the overall cost of the operation. Moreover, the overall quality of the liquid product from a catalytic hydroconversion has, in general, been poor due primarily to its higher molecular weight and lower hydrogen content. The need, then, for an improved catalytic process which will yield improved quality liquid products and higher yields of gasoline boiling range liquid is believed to be readily apparent.